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clock_settime(3) [osf1 man page]

clock_gettime(3)					     Library Functions Manual						  clock_gettime(3)

NAME
clock_gettime, clock_settime - Obtains or sets the time for the specified clock (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <time.h> int clock_gettime ( clockid_t clock_id, struct timespec *tp); int clock_settime ( clockid_t clock_id, const struct timespec *tp); PARAMETERS
clock_id The clock type used to obtain the time for the clock that is set. The CLOCK_REALTIME clock is supported and represents the TIME-OF-DAY clock for the system. *tp A pointer to a timespec data structure. DESCRIPTION
The clock_gettime function returns the current time (in seconds and nanoseconds) for the specified clock. The clock_settime function sets the specified clock. The CLOCK_REALTIME clock measures the amount of time elapsed since 00:00:00:00 January 1, 1970 Greenwich Mean Time (GMT), otherwise known as the Epoch. Time values that fall between two non-negative integer multiples of the resolution are truncated down to the smaller multiple of the resolution. You must have superuser privileges to use the clock_settime function. RETURN VALUES
On a successful call to the clock_gettime or clock_settime functions, a value of 0 (zero) is returned. On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. ERRORS
The clock_gettime and clock_settime functions fail under the following conditions: [EINVAL] The clock_id argument does not specify a known clock. The value pointed to by the tp argument to the clock_settime function is outside the range for the given clock_id. The tp argument specified a nanosecond value less than zero or greater than or equal to 1000 million. [EPERM] The requesting process does not have the appropriate privilege to set the specified clock. RELATED INFORMATION
Functions: time(1), clock_getres(3), ctime(3), timer_gettime(3) Guide to Realtime Programming delim off clock_gettime(3)

Check Out this Related Man Page

CLOCK_SETTIME(2)					      BSD System Calls Manual						  CLOCK_SETTIME(2)

NAME
clock_settime, clock_gettime, clock_getres -- clock and timer functions LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <time.h> int clock_settime(clockid_t clock_id, const struct timespec *tp); int clock_gettime(clockid_t clock_id, struct timespec *tp); int clock_getres(clockid_t clock_id, struct timespec *res); DESCRIPTION
The clock_settime() function sets the clock identified by clock_id to the absolute time specified by tp. If the time specified by tp is not a multiple of the resolution of the clock, tp is truncated to a multiple of the resolution. The clock_gettime() function stores the time of the clock identified by clock_id into the location specified by tp. The clock_getres() function stores the resolution of the clock identified by clock_id into the location specified by res, unless res is NULL. A clock_id of CLOCK_REALTIME identifies the realtime clock for the system. For this clock, the values specified by clock_settime() and obtained by clock_gettime() represent the amount of time (in seconds and nanoseconds) since 00:00 Universal Coordinated Time, January 1, 1970. A clock_id of CLOCK_MONOTONIC identifies a clock that increases at a steady rate (monotonically). This clock is not affected by calls to adjtime(2) and settimeofday(2) and will fail with an EINVAL error if it's the clock specified in a call to clock_settime(). The origin of the clock is unspecified. If the calling user is not the super-user, then the clock_settime() function in the standard C library will try to use the clockctl(4) device if present, thus making possible for non privileged users to set the system time. If clockctl(4) is not present or not accessible, then clock_settime() reverts to the clock_settime() system call, which is restricted to the super user. RETURN VALUES
A value of 0 is returned on success. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
The clock_settime(), clock_gettime() and clock_getres() functions will fail if: [EINVAL] The clock_id argument does not specify a known clock. [ENOSYS] The function is not supported by this implementation. The clock_settime() function will fail if: [EINVAL] The tp argument is outside the range for the specified clock, clock_id. [EINVAL] The tp argument specified a nanosecond value less than zero of greater than or equal 1000 million. [EINVAL] The clock_id argument is a clock that can not be adjusted. [EPERM] The calling process does not have the appropriate privilege to set the specified clock, clock_id. The clock_gettime() function will fail if: [EFAULT] The tp argument specifies an address that is not a valid part of the process address space. SEE ALSO
ctime(3), time(3), clockctl(4) STANDARDS
The clock_settime(), clock_gettime() and clock_getres() functions conform to IEEE Std 1003.1b-1993 (``POSIX.1''). BSD
February 11, 1999 BSD
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